The invention relates to frost-stable aqueous alkaline solutions of highly concentrated o-phenylphenol and to their use as preservatives.
Orthophenylphenol (OPP) is an important active compound for preparing preservatives for protecting industrial materials such as, inter alia, glues or adhesives, concrete additives, cooling lubricants, pigment slurries. It is the intended function of preservatives for industrial materials to protect the treated products against microbial degradation. For this purpose, the preservatives have to be predominantly in the aqueous phase to reach the microorganisms living there. Accordingly, it is a precondition for preservatives to be effective that they are sufficiently water-soluble.
However, for preservatives based on phenolic active compounds, this is not always the case to the desired degree. Thus, for example, the solubility of the active compound o-phenylphenol (cf., for example, W. Paulus, xe2x80x9cMicrobicides for the Protection of Materials,xe2x80x9d Chapman and Hall, 1993, page 170 ff.) in neutral water is only 0.02% by weight. To incorporate this active compound without any problems into industrial materials, it is therefore necessary to pre-dissolve the microbially active compound first, to convert it into a form which is better suitable for further processing. In practice, this is usually achieved by preparing a solution in alkaline solutions (aqueous sodium hydroxide solution, aqueous potassium hydroxide solution), alcohols, glycols and the like, followed by addition of the required amount of the resulting liquid biocide product to the product to be protected. From application points of view, it is particularly advantageous to convert OPP into the corresponding phenolate by neutralization with bases (for example LiOH, NaOH, KOH, Ca(OH)2), since the alkali metal salts or alkaline earth metal salts of OPP have a considerably better solubility in water than free OPP.
The method of forming a presolution in aqueous sodium hydroxide solution, a method which is already known and widely used, is associated with the problem that, with an increasing active compound content (calculated for OPP), even at relatively low OPP concentrations, solutions are obtained which have a crystallization point which is too high for practical application. Owing to crystallization, which in some cases occurs even at temperatures above 0xc2x0 C., it is difficult to use such solutions in a controlled manner in industrial practice, in particular during the cold time of year, when undesirable solidification of the biocide product in storage tanks, pipelines and pumps may occur. This process requires time-consuming and costly measures for re-liquefying the biocide product and may result in production down-times. In addition, an uncontrolled solidification in pipelines and pumps may lead to a build up of pressure and leakages which, from the point of view of operational safety, causes a risk.
The tendency of aqueous solutions of o-phenylphenol (OPP) in aqueous NaOH to crystallize is shown in the table below
To provide more highly concentrated solutions of OPP in alkaline media, solutions in aqueous potassium hydride solution have been described, in addition to the solutions in aqueous sodium hydroxide solution described above. However, only mixtures of a maximum concentration of up to 30% by weight of OPP have been prepared and used commercially to date. In addition to the excess of alkali of the known 30% strength OPP solution, which is too high for many applications, the active compound content of this formulation is, with respect to optimum logistics, still too low, since shipping and internal company logistics require large quantities of water to be moved, which leads to an uneconomical operation and moreover appears to be worthy of improvement from an ecological point of view.
Accordingly, it is the object of the present invention to provide aqueous alkaline solutions of OPP which do not have the above-described disadvantages of the known solutions.
In particular, it is an object to provide more highly concentrated solutions ( greater than 30% by weight of OPP) of OPP in aqueous-alkaline media such as aqueous solutions of LiOH, NaOH, KOH or Ca(OH)2 and binary mixtures of these alkaline media which remain stable for the duration of storage and use even at temperatures below 0xc2x0 C., without any crystallization taking place.
Surprisingly, it has now been found that concentrated solutions of OPP salts in water, which are crystallization-stable (frost-stable) even at low temperatures, are obtained when the components are mixed in certain ratios.
The invention relates to a mixture comprising (i) water, (ii) o-phenylphenol and (iii) a base component, wherein the o-phenylphenol and the base component are at a molar ratio ranging from 1:1.02 to 1:1.10 and the o-phenylphenol is present in the mixture at 45% by weight. The invention also relates to a process comprising (A) mixing (i) water, (ii) o-phenylphenol and (iii) a base component, and (B) forming a mixture comprising (i) water, (ii) o-phenylphenol and (iii) a base component, wherein the o-phenylphenol and the base component are at a molar ratio ranging from 1:1.02 to 1:1.10 and the o-phenylphenol is present in the mixture at 45% by weight. The invention also relates to a method comprising (A) treating an industrial material comprising water, o-phenylphenol and a base component, wherein the o-phenylphenol and the base component are at a molar ratio ranging from 1:1.02 to 1:1.10 and the o-phenylphenol is present in the mixture at 45% by weight, and (B) protecting the industrial material. These and other features, aspects, and advantages of the present invention will become better understood with reference to the following description and appended claims.